Meaty question

After cooking beef, and then refrigerating it uncovered for a week, is there any bacteria that grows back/comes back alive from inside the meat? Or does cooking destroy those critters for good?

it destroys them for good… but there are lots of bacteria in the world, they are easly replaced. the ones you kill won’t be back, but meat thats been cooked can easyly get rancid

Cooking it to 160 degrees F (71C) kills bacteria, so I don’t think you’ll have anything reanimate from within the meat. But that doesn’t mean that cooked meat can’t harbor bacteria. Especially uncovered, especially after a week. Bacteria is all around you, man. And cooked meat is a good nutrient medium for it. Meat will pick up bacteria from touching preparation surfaces or just from the air. Mold spores are probably more plentiful, though you can see mold growing pretty readily.

Cooking meat properly means killing all the bacteria therein. I’m sure someone has got an experiment going to see if life will reassert itself in the ruptured carcasses of single-cell life (I’m sure you’ve read about the staggering improbability of life self-arranging on the Early Earth. I imagine it would be easier with the appropriate pieces floating in immense quantities in a small, warm space)
Your fridge is NOT clean nor sealed. There definitely are living microorganisms in your fridge, and they are definitely on your food, happily reproducing, the moment you put it in. There’s also probably enough to make you sick, after a week uncovered. Even if you put it in a sterile, airtight container container a week ago and showered the container with gamma raays, I’d cook it before eating it.
Always cook meat shortly before you eat it. That’s my rule. Don’t hoard stuff that readily rots, i.e. eat it before it starts going bad and don’t buy enough that it goes bad before you’ve finished eating it all.

Not to mention the fact that leaving cooked meat in the refrigerator, uncovered, for a week would make it extremely dehydrated. It would be like trying to eat a hockey puck. Throw it out.